Quality control can only be done on the stone based on criteria established by the buyer.
Quality is not an issue of stone selection, and even though a stone may be a second or commercial rating, that does not mean the stone is of poor quality. Quality is definable like the tolerance of the thickness, sizing tolerances, squareness etc.
Many buyers request on major projects and/or purchases to have goods inspected. This is a very good safety factor to have and should be budgeted into most purchase orders. It is important to have the inspector know the selection and criteria required for each order which should include copies of the purchase order, samples of the stone selected and the range accepted in the stone, the stone supplier, drawings and copies of shop tickets, sizes and finishes and details of anything that is important to verify.
What do you expect from an inspector? Normally a check list of items to be inspected is a good thing to have ready for the inspector to make sure he/she is investigating all issues. These can include but are not limited to: Tolerances, degree of finishing, edgework, eased edges, whether you accept pits, open seams, small and large fissures, stress marks, iron spots, other marks not in the samples approved, or veins of certain size and length or color. Also, squareness or shape of the stone, and whether it meets the templates submitted as in the case of radius stone walls or pavers, special shapes, anchor hole or slots, kerfs, and size, tolerances and locations, chipped edges or corners, blending or book-matching if required, dry layouts, photos of the stones or patterns, joint sizes, and many other factors. Working with a stone consultant to establish the criteria is important to have a proper inspection made and accepted.
In some cases payment is only authorized by the buyer if a copy of the stone inspection report signed by the inspector is submitted as part of the documents for payment on each shipment. Further issues must be included such as time frame for shipping and sequencing of the job, packing in crates, loading and bracing in the containers and ship dates should all be checked.
Everything is an option and because a stone has more or less veins, pits, seams, fissures has no meaning as to the quality of the stone. Many stones even require re-gluing of broken pieces such as black and gold marble, and if done properly this is an acceptable and normal practice and does not mean the stone is to be rejected or is inferior, but is the nature of the stone selected. The buyer needs to know about the natural range and variation of the stone and the issues with markings, veining, pits, fissures etc. and make sure their client is knowledgeable of the issues so there are no surprises when the stone arrives and is installed.
A good stone consultant can communicate these issues and set up the parameters and help with the inspections. Trade International has access to, and works in most countries, with inspectors when requested by the buyer and/or may demand that one be hired in order to facilitate the job quality controls and delivery of stone.